High-voltage supply for cathode-ray tubes



Feb. 1o', 1953 B. S. VILKOMERSON HIGH VOLTAGE SUPPLY FOR CATHODE-RAY TUBES Filed Aug. l0, 1951 INVENTOR Patented Feb. 10, `1953 UNITED STATES HIGH-VOLTAGE SUPPLY FOR CATHODE-RAY TUBES Benjamin S. Vilkomerson, Camden, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application August 10, 1951, Serial No. 241,321

4 Claims.

Y This invention relates to variable high voltage supply systems, and particularly, to systems for supplying an adjustable voltage of high magnitude between the cathode and another electrode of a cathode ray tube.

In apparatus employing cathode ray tubes of the electrostatic focusing type, it is customary to apply very high unidirectional positive potential to the second anode and a somewhat lower, adjustable, unidirectional positive potential to the first or focusing anode of the cathode ray tube. The iirst anode potential is made adjustable so that the cathode beam may be brought into focus. Thus, in a television receiver employing an electrostatically focused cathode ray tube, the focus adjustment in effect varies the potential impressed upon the first or focusing anode.

Heretofore it has been the usual practice to obtain the focusing potential by means of a conventional potentiometer voltage divider. Such a potentiometer arrangement is expensive, involves difficulties in insulating it for the high voltages involved and has the further disadvantages of drawing an appreciable amount of current thereby draining power from the source, and of giving poor voltage regulation.

It is accordingly one object of this invention to provide an improved method of and means for obtaining an adjustable unidirectional high voltage with a wide range of adjustment.

It is another object of this invention to provide an improved method of and means for obtaining an adjustable unidirectional high voltage with a wide range of adjustment for the focusing anode of a cathode ray tube.

According to the present invention, a high alternating potential is adjusted by means of a capacitance voltage divider, two elements of which are elements of a differential capacitor. This adjusted alternating potential is rectified and applied to the focusing anode of the cathode ray tube. A differential capacitor is one having two elements, one of which can be made to increase in capacitancewhile the other is decreased.

Other and incidental objects of this invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing, in which:

Figure 1 is a schematic representation of a cathode ray tube power supply circuit embodying the invention, and

Figure 2 is a sectional view of a capacitor suitable for use in the circuit shown in Figure 1.

Referring to Figure l, this invention is shown applied to a television receiver I which includes an electrostatic focus picture tube 2. The particular picture tube illustrated is of a well known type comprising an evacuated envelope 3 having an electron gun therein which comprises a cathode 5, a control grid 1, and a first or focusing anode 9. A second anode Il, consisting of conductive coating on the inside of the envelope 3, is provided for accelerating the electrons and for aiding in electrostatic focusing. The usual fiuorescent screen I3 is provided at the large end of the tube.

In accordance with common practice, the picture tube is provided with one pair of deflecting coils I5 for deiiecting the electron beam horizontally, and another pair of deflecting coils I'I for dellecting the electron beam vertically, whereby the fluorescent screen I3 may be scanned to produce a picture. Details relating to the television receiver and vertical deflection are not illustrated as any of the usual types may be employed, such as, for example. those shown and described in an article by A. Wright in RCA Re- View for March 1947.

A horizontal sweep oscillator I9 supplies a saw tooth potential to the grid of the horizontal sweep output tube 2| which in turn supplies a saw tooth current component to the output transformer 23. During the horizontal trace the deflection current increases linearly in the horizontal deection coils I5, and a corresponding magnetic field is produced. During the retrace period the output tube 2l is cut oif, and the sudden removal of plate current causes a sudden collapse of the magnetic field. This collapse in turn causes a high amplitude transient voltage pulse to appear across the horizontal deflection coils I5. A damper tube 25 prevents this transient voltage pulse from setting up a series of oscillations.

This high amplitude pulse which has a peak amplitude of the order of several thousand volts, is stepped up by the horizontal output transformer 23. A high voltage rectifier 21 is connected between the high voltage terminal of transformer 23 and the second anode II of cathode ray tube 2. The high voltage rectifier 2T recties this transient voltage to produce, after filtering by capacitor 29 and a resistor 30, a constant high voltage potential. The filament of the high voltage rectifier 21 is energized by means of a few turns of wire 3l wound on the core of the horizontal output transformer 23.

The rst or focusing anode potential, which must be adjustable, is obtained as follows. A high voltage rectifier 32 has its plate (or anode) connected to tap 33 of the horizontal output transformer 23. The lament (or cathode) of rectifier 32 is energized by means of a few turns of wire 34 wound on the core of the horizontal output transformer 23.

In accordance with the present invention a differential capacitor 35 has its element 36 connected between the anode and the cathode of the rectifier 32 and its element 31 connected between the cathode of rectifier 32 and a point of reference potential such as ground.

The interelectrode capacitance of rectifier 32 has been shown at 38, while the stray capacitance between ground and the winding of the lament of rectifier 32 has been shown at 39. The filament of rectifier 32 is connected to a lter network comprising resistor 4l and capacitor 43, and by means of lead i5 to the focusing anode 9 of the kinescope Il.

The opei'ation of the circuit is as follows: the focusing anode Voltage is determined by the potential between points 33 and 41. The potential at point i1 is determined by the relative values of the capacitance between points 33 and 31 and of the capacitance between points 41 and ground, these two capacitances forming a voltage divider. The capacitance between points 33 and i1 comprises capacitances 33 and 33. The capacitance between point i1 and ground comprises capacitances 31 and 39. A wide range of adjustment of the focusing anode Voltage is obtainable by using the differential capacitor 35, as will be brought out by the following numerical example.

Let us assume the following circuit values: capacitances 33 and 3Q: l mmf.; capa-citances 33 and 31: 2 to 40 mmf.; and peak plate voltage of rectifier 32: 6000 volts.

At the minimum value of capacitance 32 and the maximum value of ycapacitance 3i the potential at point 41 will be:

Volts At the maximum value of capacitance 33 and the minimum value of capacitance 3i, the potential at point 41 will be:

Figure 2 shows a differential capacitor suitable for use in the circuit of Figure l. A ceramic tube 49 of high dielectric constant material is mounted on a block of insulating material i which is used as the mechanical support for the assembly. The inner electrode of the capacitor is the piston 53, the position of which is controlled by rotating the threaded stud 55 in the tapped metal plate 5i. Electrical contact between the outside circuit (point il of Figure 1) and the piston is maintained by means of lead 5S?. Electrodes 35 and 3'." are the outer electrodes of the capacitor and in coniunction with piston 53 form capacity elements 33 and 31 of differential capacitor 35 of Figure l.

When by rotating the stud 55 clockwise, the piston 53 is moved away from electrode 31' and under electrode 33', the interelectrode capacitance of the rectifier is effectively increased, and the capacitance between the filament of rectifier 32 and ground is decreased; the source voltage seen by the rectifier is decreased, and the focusing anode Voltage is decreased.

When by rotating the stud 55 counterclockwise, the piston 53 is moved away from electrode 3% and under electrode 31', the interelectrode capacitance of the rectifier is effectively decreased, the 4capacitance between the filament of rectier 32 and ground is increased, and the focusing anode voltage is increased.

A heavy coating of Silicone grease between the piston 53 and the dielectric tube 49, by filling up the air gap between the piston and the tube, eliminates corona and increases the maximum :403 Volts effective capacitance of the differential capacitor.

I claim:

l. A high voltage power supply for` an electrcstatcally focused cathode ray tube, said high voltage power supply comprising a transformer, a rectifier having two electrodes, means connecting said rectier to said transformer` a point of reference potential, a differential capacitor having two elements, means connecting one element of said differential capacitor between the electrodes of said rectifier, and means connecting another element of said differential capacitor between one electrode of said rectier and said point of reference potential.

2. A high voltage power supply for an electrostatically focused cathode ray tube having a focus electrode, said high voltage power supply comprising a transformer, `a rectifier having two electrodes, means connecting said rectifier to said transformer, a point of reference potential, a differential capacitor having two elements, means connecting one element of said differential capac'itor between the electrodes of said rectifier, means connecting another element of said differential capacitor between one electrode of said rectifier and said point of reference potential, and means connecting said last named electrode of said rectifier to said focus electrode.

3. A high voltage power'supply for an electrostatically focused cathode ray tube having a focus electrode, said high voltage power supply comprising a transformer, a rectifier having an anode and a cathode, means connecting the anode of said rectifier to said transformer, a point of reference potential, a differential capacitor having two ele'- ments, means connecting one element of said differential capacitor between the anode and the cathode of said rectifier, means connecting another element of said differential capacitor between the cathode of said rectifier and said point of reference potential, and means connecting the cathode of said rectifier to said focus electrode.

4. A high voltage power supply for an electrostatically focused cathode ray tube having a first anode and a second anode, said high Voltage power supply comprising a transformer, a rst rectifier having an anode and a cathode, means connecting the anode of said first rectifier to said transformer, means connecting the cathode of said rectifier to the second anode of said cathode ray tube, va second rectifier having an anode and a cathode, means connecting the anode of said second rectifier to said transformer, a point of reference potential, a differential capacitor having two elements, means connecting one element of said differential capacitor between the anode and the cathode of said second rectifier, means connecting another element of said differential capacitor between the cathode of said second rectifier and said point of reference potential, and means connecting the cathode of said second rectifier to the first anode of said cathode ray tube.

BENJAMIN S. VILKOMERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,218,754 Moller et al Oct. 22, 194i) 2,265,620 Bahring Dec. 9, 1941 2,397,150 Lyman Mar. 26, 1946 2,431,051 Kozanowski f Nov. 18, 1947 

